Inner focus lens, interchangeable lens apparatus and camera system

ABSTRACT

An inner focus lens, in order from an object side to an image side, comprising: a first lens unit having positive optical power; a second lens unit having negative optical power; and a third lens unit having positive optical power, wherein the second lens unit is moved along an optical axis so that focusing from an infinite-distance object side to a short-distance object side is achieved, the first lens unit includes a bi-convex air lens, and the following conditions: 0.65&lt;|f 2 /f|&lt;5.00 and 0.5&lt;f 23 /f 1 &lt;9.0 (f 2 : a focal length of the second lens unit, f and f 23 : a focal length of the entire system and a composite focal length of the second and third lens units in an infinity in-focus condition, f 1 : a focal length of the first lens unit) are satisfied; an interchangeable lens apparatus; and a camera system are provided.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on application No. 2011-085154 filed in Japanon Apr. 7, 2011 and application No. 2012-040218 filed in Japan on Feb.27, 2012, the contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to inner focus lenses, interchangeablelens apparatuses, and camera systems. Specifically, the presentinvention relates to: inner focus lenses suitable for an interchangeablelens apparatus attachable to a digital single-lens reflex camera or asingle-lens reflex camera using silver salt films, a digital stillcamera, a camcorder, and the like; and interchangeable lens apparatusesand camera systems employing these inner focus lenses.

2. Description of the Background Art

In association with increases in the number of pixels of solid-stateimage sensors in recent years, imaging optical systems employed for themare requested to have higher performance as well as to be a bright lenshaving a small F-number. Further, strong demands are present forhigher-speed focusing and for lenses in which image vibration at thetime of focusing is reduced. Moreover, strong demands are present alsofor size reduction and cost reduction in the optical systems, and hencesuch optical systems are requested to be constructed from a small numberof lenses.

In order that such demands should be satisfied, a lens system disclosedin Japanese Laid-Open Patent Publication No. S50-138823 has beenproposed which is a so-called Gauss type lens system, in order from theobject side to the image side, comprising a front lens unit havingpositive refractive power and a rear lens unit having positiverefractive power and in which focusing is achieved by a positive lensunit included in the rear lens unit. In such a Gauss type lens system, alarge aperture is implemented and yet, compensation of aberration isachieved easily.

However, in the lens system disclosed in Japanese Laid-Open PatentPublication No. S50-138823, focusing is performed by the positive lensunit included in the rear lens unit. This causes an increase in theamount of movement of the positive lens unit at the time of focusing,and hence high-speed focusing demanded in recent years is not realized.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an inner focus lenshaving a large aperture and yet capable of high-speed focusing; and aninterchangeable lens apparatus and a camera system employing this innerfocus lens.

The novel concepts disclosed herein were achieved in order to solve theforegoing problems in the conventional art, and herein is disclosed:

an inner focus lens, in order from an object side to an image side,comprising:

a first lens unit having positive optical power;

a second lens unit having negative optical power; and

a third lens unit having positive optical power, wherein

the second lens unit is moved along an optical axis so that focusingfrom an infinite-distance object side to a short-distance object side isachieved,

the first lens unit includes a bi-convex air lens, and

the following conditions (1) and (2) are satisfied:

0.65<|f ₂ /f|<5.00  (1)

0.5<f ₂₃ /f ₁<9.0  (2)

where,

f₂ is a focal length of the second lens unit,

f is a focal length of the entire system in an infinity in-focuscondition,

f₂₃ is a composite focal length of the second lens unit and the thirdlens unit in an infinity in-focus condition, and

f₁ is a focal length of the first lens unit.

The novel concepts disclosed herein were achieved in order to solve theforegoing problems in the conventional art, and herein is disclosed:

an interchangeable lens apparatus comprising:

an inner focus lens; and

a lens mount section which is connectable to a camera body including animage sensor for receiving an optical image formed by the inner focuslens and converting the optical image into an electric image signal,wherein

the inner focus lens, in order from an object side to an image side,comprises:

a first lens unit having positive optical power;

a second lens unit having negative optical power; and

a third lens unit having positive optical power, wherein

the second lens unit is moved along an optical axis so that focusingfrom an infinite-distance object side to a short-distance object side isachieved,

the first lens unit includes a bi-convex air lens, and

the following conditions (1) and (2) are satisfied:

0.65<f ₂ /f|<5.00  (1)

0.5<f ₂₃ /f ₁<9.0  (2)

where,

f₂ is a focal length of the second lens unit,

f is a focal length of the entire system in an infinity in-focuscondition,

f₂₃ is a composite focal length of the second lens unit and the thirdlens unit in an infinity in-focus condition, and

f₁ is a focal length of the first lens unit.

The novel concepts disclosed herein were achieved in order to solve theforegoing problems in the conventional art, and herein is disclosed:

a camera system comprising:

an interchangeable lens apparatus including an inner focus lens; and

a camera body which is detachably connected to the interchangeable lensapparatus via a camera mount section, and includes an image sensor forreceiving an optical image formed by the inner focus lens and convertingthe optical image into an electric image signal, wherein

the inner focus lens, in order from an object side to an image side,comprises:

a first lens unit having positive optical power;

a second lens unit having negative optical power; and

a third lens unit having positive optical power, wherein

the second lens unit is moved along an optical axis so that focusingfrom an infinite-distance object side to a short-distance object side isachieved,

the first lens unit includes a bi-convex air lens, and

the following conditions (1) and (2) are satisfied:

0.65<f ₂ /f|<5.00  (1)

0.5<f ₂₃ /f ₁<9.0  (2)

where,

f₂ is a focal length of the second lens unit,

f is a focal length of the entire system in an infinity in-focuscondition,

f₂₃ is a composite focal length of the second lens unit and the thirdlens unit in an infinity in-focus condition, and

f₁ is a focal length of the first lens unit.

The present invention provides: an inner focus lens in which theconstruction is realized by a small number of lens elements and yetvarious kinds of aberrations are compensated satisfactorily and in whichthe amount of movement of a focusing lens unit at the time of focusingis small and the focusing lens unit has a light weight and hence,although a large aperture is implemented, high-speed focusing isachieved; and an interchangeable lens apparatus and a camera systememploying this inner focus lens.

BRIEF DESCRIPTION OF THE DRAWINGS

This and other objects and features of this invention will become clearfrom the following description, taken in conjunction with the preferredembodiments with reference to the accompanied drawings in which:

FIG. 1 is a lens arrangement diagram showing an infinity in-focuscondition of an inner focus lens according to Embodiment 1 (Example 1);

FIG. 2 is a longitudinal aberration diagram of an infinity in-focuscondition of an inner focus lens according to Example 1;

FIG. 3 is a lens arrangement diagram showing an infinity in-focuscondition of an inner focus lens according to Embodiment 2 (Example 2);

FIG. 4 is a longitudinal aberration diagram of an infinity in-focuscondition of an inner focus lens according to Example 2;

FIG. 5 is a lens arrangement diagram showing an infinity in-focuscondition of an inner focus lens according to Embodiment 3 (Example 3);

FIG. 6 is a longitudinal aberration diagram of an infinity in-focuscondition of an inner focus lens according to Example 3;

FIG. 7 is a lens arrangement diagram showing an infinity in-focuscondition of an inner focus lens according to Embodiment 4 (Example 4);

FIG. 8 is a longitudinal aberration diagram of an infinity in-focuscondition of an inner focus lens according to Example 4;

FIG. 9 is a lens arrangement diagram showing an infinity in-focuscondition of an inner focus lens according to Embodiment 5 (Example 5);

FIG. 10 is a longitudinal aberration diagram of an infinity in-focuscondition of an inner focus lens according to Example 5;

FIG. 11 is a lens arrangement diagram showing an infinity in-focuscondition of an inner focus lens according to Embodiment 6 (Example 6);

FIG. 12 is a longitudinal aberration diagram of an infinity in-focuscondition of an inner focus lens according to Example 6; and

FIG. 13 is a schematic construction diagram of an interchangeable-lenstype digital camera system according to Embodiment 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An inner focus lens according to the present invention, in order from anobject side to an image side, comprises a first lens unit havingpositive optical power, a second lens unit having negative opticalpower, and a third lens unit having positive optical power. Then, thesecond lens unit is moved along an optical axis so that focusing from aninfinite-distance object side to a short-distance object side isachieved. Further, the first lens unit includes a bi-convex air lens.Here, an air space between two lens elements is regarded as a lenshaving a refractive index of approximately 1, and the air space isreferred to as an air lens.

In the lens configuration of the inner focus lens according to thepresent invention, by virtue of light-beam converging operation achievedby the positive optical power of the first lens unit, the lens outerdiameter of the second lens unit serving as a focusing lens unit can bereduced. Thus, weight reduction is achieved in the focusing lens unit.Further, when the focusing lens unit is driven by an auto-focusingmechanism based on electric lens drive, high-speed focusing is achieved.

In the above-mentioned lens configuration, on the object side and theimage side relative to the second lens unit having negative opticalpower and serving as a focusing lens unit, the first lens unit havingpositive optical power and the third lens unit having positive opticalpower are arranged, respectively. This enhances magnification of thesecond lens unit. As a result, the amount of movement of the focusinglens unit is reduced. Thus, when the focusing lens unit is driven by anauto-focusing mechanism based on electric lens drive, high-speedfocusing is achieved.

In the above-mentioned lens configuration, on the image side relative tothe second lens unit having negative optical power, the third lens unithaving positive optical power is arranged. Thus, without the necessityof increasing back distance of the inner focus lens, the exit pupilposition can be located at a position farther from an image surface. Asa result, when the inner focus lens is applied to a camera provided witha solid-state image sensor, light-condensing performance of micro lensesprovided in front of the solid-state image sensor can be utilizedsatisfactorily.

In the above-mentioned lens configuration, the first lens unit havingpositive optical power includes a bi-convex air lens. Thus, in the innerfocus lens, a large aperture is implemented and yet, even a small numberof lens elements can easily compensate spherical aberration,astigmatism, and the like so as to reduce the remaining aberration inthe first lens unit as small as possible. As a result, contribution tocompensation of aberration of the second lens unit serving as a focusinglens unit decreases and hence the second lens unit is allowed to beconstructed from a small number of lens elements. Thus, weight reductionof the focusing lens unit and size reduction of the inner focus lens areachieved.

In the above-mentioned lens configuration, it is preferable that thesecond lens unit is composed of a single unit having negative opticalpower like a cemented lens element having negative optical power or asingle lens element having negative optical power. Further, it is morepreferable that the single unit having negative optical power iscomposed of one single lens element having negative optical power. Inthis case, further weight reduction of the focusing lens unit andfurther size reduction of the inner focus lens are achieved.

In the inner focus lens according to the present invention, thefollowing condition (1) is satisfied.

0.65<f ₂ /f|<5.00  (1)

where,

f₂ is a focal length of the second lens unit, and

f is a focal length of the entire system in an infinity in-focuscondition.

The condition (1) sets forth the ratio between the focal length of thesecond lens unit and the focal length of the entire system of the innerfocus lens. When the value goes below the lower limit of the condition(1), the optical power of the second lens unit becomes strong and henceit becomes difficult to construct the second lens unit from a smallnumber of lens elements. On the other hand, when the value exceeds theupper limit of the condition (1), the optical power of the second lensunit becomes weak and hence the amount of movement at the time offocusing increases. This prevents high-speed focusing and size reductionin the inner focus lens.

When at least one of the following conditions (1)′ and (1)″ issatisfied, the above-mentioned effect is achieved more successfully.

0.68<|f ₂ /f|  (1)′

|f ₂ /f|<4.00  (1)″

In the inner focus lens according to the present invention, in additionto that the condition (1) is satisfied, the following condition (2) issatisfied.

0.5<f ₂₃ /f ₁<9.0  (2)

where,

f₂₃ is a composite focal length of the second lens unit and the thirdlens unit in an infinity in-focus condition, and

f₁ is a focal length of the first lens unit.

The condition (2) sets forth the ratio between the composite focallength of the second lens unit and the third lens unit, and the focallength of the first lens unit. When the value goes below the lower limitof the condition (2), the optical power of the first lens unit becomesweak and hence size increase becomes unavoidable in the first lens unit.This prevents size reduction of the inner focus lens. On the other hand,when the value exceeds the upper limit of the condition (2), thecomposite optical power of the second lens unit and the third lens unitbecomes weak. This prevents a larger-aperture construction of the innerfocus lens.

When at least one of the following conditions (2)′ and (2)″ issatisfied, the above-mentioned effect is achieved more successfully.

1.5<f ₂₃ /f ₁  (2)′

f ₂₃ /f ₁<6.0  (2)″

In the inner focus lens according to the present invention, it ispreferable that the first lens unit includes a bi-convex air lens havingan object side “a” surface and an image side “b” surface and that thefollowing condition (3) is satisfied.

−0.5<SF<0.5  (3)

where,

SF=(Ra+Rb)/(Rb−Ra),

Ra is a radius of curvature of an object side “a” surface of thebi-convex air lens included in the first lens unit, and

Rb is a radius of curvature of an image side “b” surface of thebi-convex air lens included in the first lens unit.

The condition (3) sets forth the shape of the bi-convex air lensincluded in the first lens unit. The condition (3) indicates that theabsolute value of the radius of curvature of the object side “a” surfaceis close to the absolute value of the radius of curvature of the imageside “b” surface. When the condition (3) is satisfied, various kinds ofaberrations such as spherical aberration and astigmatism generated inthe first lens unit can be compensated satisfactorily by a small numberof lens elements.

When at least one of the following conditions (3)′ and (3)″ issatisfied, the above-mentioned effect is achieved more successfully.

−0.1<SF  (3)′

SF<0.2  (3)″

In the inner focus lens according to the present invention, it ispreferable that the following condition (4) is satisfied.

0.02<D ₂ /{f×tan(ω)}<0.30  (4)

where,

D₂ is an optical axial thickness of the second lens unit,

f is a focal length of the entire system in an infinity in-focuscondition, and

ω is a half view angle (°) of the entire system in an infinity in-focuscondition.

The condition (4) sets forth the ratio between the optical axialthickness of the second lens unit and the image height. When the valuegoes below the lower limit of the condition (4), the optical axialthickness of the second lens unit becomes small and hence fabrication ofthe lens becomes difficult. On the other hand, when the value exceedsthe upper limit of the condition (4), the optical axial thickness of thesecond lens unit becomes large. This prevents weight reduction of thefocusing lens unit and size reduction of the inner focus lens.

When at least one of the following conditions (4)′ and (4)″ issatisfied, the above-mentioned effect is achieved more successfully.

0.05<D ₂ /{f×tan(ω)}  (4)′

D ₂ /{f×tan(ω)}<0.15  (4)″

It is preferable that the inner focus lens according to the presentinvention is provided with an aperture diaphragm for restricting axiallight beam and that the following condition (5) is satisfied.

0.5<f _(sb) /f<3.0  (5)

where,

f_(sb) is a composite focal length of lens elements located on the imageside relative to the aperture diaphragm in an infinity in-focuscondition, and

f is a focal length of the entire system in an infinity in-focuscondition.

The condition (5) sets forth the ratio between the composite focallength of the lens elements located on the image side relative to theaperture diaphragm in an infinity in-focus condition and the focallength of the entire system of the inner focus lens in an infinityin-focus condition. When the value goes below the lower limit of thecondition (5), the composite optical power of the lens elements locatedon the image side relative to the aperture diaphragm becomes strong andhence it becomes difficult to construct the inner focus lens from asmall number of lens elements. This prevents size reduction of the innerfocus lens. On the other hand, when the value exceeds the upper limit ofthe condition (5), the composite optical power of the lens elementslocated on the image side relative to the aperture diaphragm becomesweak. This prevents a larger-aperture construction of the inner focuslens.

When at least one of the following conditions (5)′ and (5)″ issatisfied, the above-mentioned effect is achieved more successfully.

0.7<f _(sb) /f  (5)′

f _(sb) /f<2.0  (5)″

In the inner focus lens according to the present invention, it ispreferable that the following condition (6) is satisfied.

0.2<|(1−β₂)×β₃|<0.9  (6)

where,

β₂ is a lateral magnification of the second lens unit in an infinityin-focus condition, and

β₃ is a lateral magnification of the third lens unit in an infinityin-focus condition.

The condition (6) sets forth deviation of the optical axis generates bydecentering in a direction perpendicular to the optical axis of thefocusing lens unit. When the value exceeds the upper limit of thecondition (6), deviation of the optical axis becomes large owing tobacklash generated in a direction perpendicular to the optical axis ofthe focusing lens unit during drive of the focusing lens unit. That is,the phenomenon of vibration of the image during focusing becomesremarkable and hence it becomes difficult to satisfy the lensrequirement of reduced image vibration. On the other hand, when thevalue goes below the lower limit of the condition (6), the magnificationof the second lens unit becomes close to 1 and hence the amount ofmovement at the time of focusing becomes large. This prevents sizereduction and high-speed focusing in the inner focus lens.

When at least one of the following conditions (6)′ and (6)″ issatisfied, the above-mentioned effect is achieved more successfully.

0.48<|(1−β₂)×β₃|  (6)′

|(1−β₂)×β₃|<0.86  (6)″

For example, inner focus lenses according to Embodiments 1 to 6described below satisfy all the conditions (1) to (6). The configurationof such an inner focus lens satisfying a plurality of the conditions ismost preferable. However, an inner focus lens may satisfy an individualcondition so as to achieve the corresponding effect.

Embodiments 1 to 6

Detailed embodiments for the inner focus lens according to the presentinvention are described below with reference to the drawings.

In each Fig., an asterisk “*” imparted to a particular surface indicatesthat the surface is aspheric. Symbol (+) or (−) imparted to the symbolof each lens unit corresponds to the sign of the optical power of eachlens unit. An arrow imparted to each lens unit indicates the movingdirection at the time of focusing from an infinite-distance object sideto a short-distance object side. Further, a straight line located on themost right-hand side indicates the position of an image surface S.

FIG. 1 is a lens arrangement diagram showing an infinity in-focuscondition of the inner focus lens according to Embodiment 1.

The inner focus lens according to Embodiment 1, in order from an objectside to an image side, comprises a first lens unit G1 having positiveoptical power, a second lens unit G2 having negative optical power, anda third lens unit G3 having positive optical power. In the inner focuslens according to Embodiment 1, the conditions (1) to (6) are satisfied.

The first lens unit G1, in order from the object side to the image side,comprises: a positive meniscus first lens element L1 with the convexsurface facing the object side; a negative meniscus second lens elementL2 with the stronger-curvature concave surface facing the image side; anaperture diaphragm A; a cemented lens element constructed from abi-concave third lens element L3 with the stronger-curvature concavesurface facing the object side and a bi-convex fourth lens element L4;and a bi-convex fifth lens element L5 having an aspheric image sidesurface. In the first lens unit G1, the space between the second lenselement L2 and the third lens element L3 forms a bi-convex air lens.

The second lens unit G2 comprises solely a bi-concave sixth lens elementL6 having two aspheric surfaces with the stronger-curvature concavesurface facing the image side. Then, the second lens unit G2 is moved tothe image side along the optical axis so that focusing from theinfinite-distance object side to the short-distance object side isachieved.

The third lens unit G3 comprises solely a bi-convex seventh lens elementL7.

FIG. 3 is a lens arrangement diagram showing an infinity in-focuscondition of the inner focus lens according to Embodiment 2.

The inner focus lens according to Embodiment 2, in order from an objectside to an image side, comprises a first lens unit G1 having positiveoptical power, a second lens unit G2 having negative optical power, anda third lens unit G3 having positive optical power. In the inner focuslens according to Embodiment 2, the conditions (1) to (6) are satisfied.

The first lens unit G1, in order from the object side to the image side,comprises: a positive meniscus first lens element L1 with the convexsurface facing the object side; a negative meniscus second lens elementL2 with the stronger-curvature concave surface facing the image side; anaperture diaphragm A; a bi-concave third lens element L3 with thestronger-curvature concave surface facing the object side; a bi-convexfourth lens element L4; and a bi-convex fifth lens element L5. In thefirst lens unit G1, the space between the second lens element L2 and thethird lens element L3 forms a bi-convex air lens.

The second lens unit G2 comprises solely a bi-concave sixth lens elementL6 with the stronger-curvature concave surface facing the image side.Then, the second lens unit G2 is moved to the image side along theoptical axis so that focusing from the infinite-distance object side tothe short-distance object side is achieved.

The third lens unit G3 comprises solely a bi-convex seventh lens elementL7.

FIG. 5 is a lens arrangement diagram showing an infinity in-focuscondition of the inner focus lens according to Embodiment 3.

The inner focus lens according to Embodiment 3, in order from an objectside to an image side, comprises a first lens unit G1 having positiveoptical power, a second lens unit G2 having negative optical power, anda third lens unit G3 having positive optical power. In the inner focuslens according to Embodiment 3, the conditions (1) to (6) are satisfied.

The first lens unit G1, in order from the object side to the image side,comprises: a negative meniscus first lens element L1 with thestronger-curvature concave surface facing the image side; a negativemeniscus second lens element L2 with the convex surface facing theobject side; a bi-convex third lens element L3; a positive meniscusfourth lens element L4 with the convex surface facing the object side; anegative meniscus fifth lens element L5 with the stronger-curvatureconcave surface facing the image side; an aperture diaphragm A; acemented lens element constructed from a bi-concave sixth lens elementL6 with the stronger-curvature concave surface facing the object sideand a bi-convex seventh lens element L7; and a bi-convex eighth lenselement L8. In the first lens unit G1, the space between the fifth lenselement L5 and the sixth lens element L6 forms a bi-convex air lens.

The second lens unit G2 comprises solely a negative meniscus ninth lenselement L9 with the stronger-curvature concave surface facing the imageside. Then, the second lens unit G2 is moved to the image side along theoptical axis so that focusing from the infinite-distance object side tothe short-distance object side is achieved.

The third lens unit G3 comprises solely a bi-convex tenth lens elementL10.

FIG. 7 is a lens arrangement diagram showing an infinity in-focuscondition of the inner focus lens according to Embodiment 4.

The inner focus lens according to Embodiment 4, in order from an objectside to an image side, comprises a first lens unit G1 having positiveoptical power, a second lens unit G2 having negative optical power, anda third lens unit G3 having positive optical power. In the inner focuslens according to Embodiment 4, the conditions (1) to (6) are satisfied.

The first lens unit G1, in order from the object side to the image side,comprises: a negative meniscus first lens element L1 with thestronger-curvature concave surface facing the image side; a bi-convexsecond lens element L2; a negative meniscus third lens element L3 withthe stronger-curvature concave surface facing the image side; anaperture diaphragm A; a cemented lens element constructed from abi-concave fourth lens element L4 with the stronger-curvature concavesurface facing the object side and a bi-convex fifth lens element L5;and a bi-convex sixth lens element L6. In the first lens unit G1, thespace between the third lens element L3 and the fourth lens element L4forms a bi-convex air lens.

The second lens unit G2 comprises solely a negative meniscus seventhlens element L7 with the stronger-curvature concave surface facing theimage side. Then, the second lens unit G2 is moved to the image sidealong the optical axis so that focusing from the infinite-distanceobject side to the short-distance object side is achieved.

The third lens unit G3 comprises solely a bi-convex eighth lens elementL8.

FIG. 9 is a lens arrangement diagram showing an infinity in-focuscondition of the inner focus lens according to Embodiment 5.

The inner focus lens according to Embodiment 5, in order from an objectside to an image side, comprises a first lens unit G1 having positiveoptical power, a second lens unit G2 having negative optical power, anda third lens unit G3 having positive optical power. In the inner focuslens according to Embodiment 5, the conditions (1) to (6) are satisfied.

The first lens unit G1, in order from the object side to the image side,comprises: a positive meniscus first lens element L1 with the convexsurface facing the object side; a negative meniscus second lens elementL2 with the stronger-curvature concave surface facing the image side; anaperture diaphragm A; a bi-concave third lens element L3 with thestronger-curvature concave surface facing the object side; a bi-convexfourth lens element L4; and a positive meniscus fifth lens element L5with the convex surface facing the object side. In the first lens unitG1, the space between the second lens element L2 and the third lenselement L3 forms a bi-convex air lens.

The second lens unit G2 comprises solely a bi-concave sixth lens elementL6 with the stronger-curvature concave surface facing the image side.Then, the second lens unit G2 is moved to the image side along theoptical axis so that focusing from the infinite-distance object side tothe short-distance object side is achieved.

The third lens unit G3 comprises solely a bi-convex seventh lens elementL7.

FIG. 11 is a lens arrangement diagram showing an infinity in-focuscondition of the inner focus lens according to Embodiment 6.

The inner focus lens according to Embodiment 6, in order from an objectside to an image side, comprises a first lens unit G1 having positiveoptical power, a second lens unit G2 having negative optical power, anda third lens unit G3 having positive optical power. In the inner focuslens according to Embodiment 6, the conditions (1) to (6) are satisfied.

The first lens unit G1, in order from the object side to the image side,comprises: a positive meniscus first lens element L1 with the convexsurface facing the object side; a negative meniscus second lens elementL2 with the stronger-curvature concave surface facing the image side; anaperture diaphragm A; a cemented lens element constructed from anegative meniscus third lens element L3 with the stronger-curvatureconcave surface facing the object side and a positive meniscus fourthlens element L4 with the convex surface facing the image side; and abi-convex fifth lens element L5. In the first lens unit G1, the spacebetween the second lens element L2 and the third lens element L3 forms abi-convex air lens.

The second lens unit G2 comprises solely a negative meniscus sixth lenselement L6 with the stronger-curvature concave surface facing the imageside. Then, the second lens unit G2 is moved to the image side along theoptical axis so that focusing from the infinite-distance object side tothe short-distance object side is achieved.

The third lens unit G3 comprises solely a bi-convex seventh lens elementL7.

Embodiment 7

FIG. 13 is a schematic construction diagram of an interchangeable-lenstype digital camera system according to Embodiment 7.

The interchangeable-lens type digital camera system 100 according toEmbodiment 7 includes a camera body 101, and an interchangeable lensapparatus 201 which is detachably connected to the camera body 101.

The camera body 101 includes: an image sensor 102 which receives anoptical image formed by an inner focus lens 202 of the interchangeablelens apparatus 201, and converts the optical image into an electricimage signal; a liquid crystal monitor 103 which displays the imagesignal obtained by the image sensor 102; and a camera mount section 104.On the other hand, the interchangeable lens apparatus 201 includes: aninner focus lens 202 according to any of Embodiments 1 to 6; a lensbarrel 203 which holds the inner focus lens 202; and a lens mountsection 204 connected to the camera mount section 104 of the camera body101. The camera mount section 104 and the lens mount section 204 arephysically connected to each other. Moreover, the camera mount section104 and the lens mount section 204 function as interfaces which allowthe camera body 101 and the interchangeable lens apparatus 201 toexchange signals, by electrically connecting a controller (not shown) inthe camera body 101 and a controller (not shown) in the interchangeablelens apparatus 201. In FIG. 13, the inner focus lens according toEmbodiment 1 is employed as the inner focus lens 202.

In Embodiment 7, since the inner focus lens 202 according to any ofEmbodiments 1 to 6 is employed, a compact interchangeable lens apparatushaving excellent imaging performance can be realized at low cost.Moreover, size reduction and cost reduction of the entire camera system100 according to Embodiment 7 can be achieved.

The following description is given for numerical examples in which theinner focus lenses according to Embodiments 1 to 6 are implementedpractically. In the numerical examples, the units of the length in thetables are all “mm”, while the units of the view angle are all “°”. Inthe numerical examples, the “surface number” indicates that the surfaceis the i-th surface when counted from the object side. Further, “r”denotes the paraxial radius of curvature of the i-th surface countedfrom the object side, “d” denotes the axial distance between the i-thsurface and the (i+1)-th surface, “nd” denotes the refractive index tothe d-line (wavelength: 587.6 nm) of the glass material whose objectside is the i-th surface, and “vd” denotes the Abbe number to the d-lineof the glass material whose object side is the i-th surface. Term“variable” indicates that the axial distance of the interval between thesurfaces is variable. Further, each surface marked with “*” after thesurface number i indicates an aspheric surface. The aspheric surfaceconfiguration is defined by the following expression.

$Z = {\frac{h^{2}\text{/}r}{1 + \sqrt{1 - {\left( {1 + \kappa} \right)\left( {h\text{/}r} \right)^{2}}}} + {\Sigma \; A_{n}h^{n}}}$

Here, the symbols in the formula indicate the following quantities.

Z is a distance from a point on an aspherical surface at a height hrelative to the optical axis to a tangential plane at the vertex of theaspherical surface,

h is a height relative to the optical axis,

r is a radius of curvature at the top,

κ is a conic constant, and

A_(n) is a n-th order aspherical coefficient.

FIGS. 2, 4, 6, 8, 10, and 12 are longitudinal aberration diagrams of aninfinity in-focus condition of the inner focus lenses according toNumerical Examples 1 to 6, respectively. Each longitudinal aberrationdiagram, in order from the left-hand side, shows the sphericalaberration, the astigmatism, and the distortion. In each sphericalaberration diagram, the vertical axis indicates the ratio to the openF-number (minimum F-number), and the horizontal axis indicates thedefocusing. Further, the solid line, the long dash line, and the shortdash line indicate the spherical aberration to the d-line, to the C-line(wavelength: 656.3 nm), and to the F-line (wavelength: 486.1 nm),respectively. In each astigmatism diagram, the vertical axis indicatesthe image height, and the horizontal axis indicates the focus. Further,the solid line and the dash line indicate the astigmatism in thesagittal image surface and in the meridional image surface,respectively. In each distortion diagram, the vertical axis indicatesthe image height, and the distortion is expressed in %.

The following Tables 1 to 6 show the lens data of the inner focus lensesaccording to Numerical Examples 1 to 6, respectively.

TABLE 1 (Numerical Example 1) Surface data Effective Surface number r dnd vd diameter Object surface ∞ 1 18.74540 4.20230 1.88300 40.8 10.699 268.34600 0.58830 9.850 3 39.42090 1.20000 1.51198 54.6 8.840 4 10.027105.97820 7.316 5(Diaphragm) ∞ 5.64000 6.953 6 −11.03380 1.00000 1.8051825.5 7.078 7 34.67830 6.54960 1.88300 40.8 8.805 8 −17.84130 0.100009.665 9 37.38830 4.20550 1.80139 45.4 10.100 10* −32.91630 Variable10.092 11* −126.83080 1.00000 1.68893 31.2 9.000 12* 27.17400 Variable9.092 13  114.19150 3.92620 1.83480 42.7 10.974 14  −33.79120 (BF)11.194 Image surface ∞ Aspherical data Surface No. 10 K = 0.00000E+00,A4 = 2.11487E−05, A6 = −4.74672E−08, A8 = 2.19448E−10 A10 =−5.03837E−13, A12 = 0.00000E+00 Surface No. 11 K = 0.00000E+00, A4 =3.62979E−05, A6 = −4.48579E−07, A8 = 2.76766E−09 A10 = −7.32635E−12, A12= 2.28019E−15 Surface No. 12 K = 0.00000E+00, A4 = 4.29240E−05, A6 =−4.05961E−07, A8 = 2.90164E−09 A10 = −1.27839E−11, A12 = 3.16035E−14Various data Focal length 25.6692 F-number 1.44319 View angle 22.9335Image height 10.8150 Overall length of lens 60.5607 BF 18.03332 Axialdistance data d0 ∞ 938 238 d10 1.9100 2.5773 4.5173 d12 6.2273 5.55993.6200 Single lens data Lens Initial surface Focal element number length1 1 28.1345 2 3 −26.6341 3 6 −10.2953 4 7 14.1701 5 9 22.4406 6 11−32.3981 7 13 31.6167 Lens unit data Front Back Initial Overallprincipal principal Lens surface Focal length points points unit No.length of lens position position 1 1 23.59025 29.46390 28.45049 28.342072 11 −32.39815 1.00000 0.48633 0.89580 3 13 31.61672 3.92620 1.671403.43160 Magnification of lens unit Lens Initial unit surface No. ∞ 1000300 1 1 0.00000 −0.02502 −0.09714 2 11 2.62843 2.61210 2.56276 3 130.41398 0.41324 0.41140

TABLE 2 (Numerical Example 2) Surface data Effective Surface number r dnd vd diameter Object surface ∞ 1 20.30060 3.93000 1.83481 42.7 9.322 289.46490 0.15000 8.444 3 16.07300 1.04510 1.50846 56.3 7.240 4 9.722705.52680 6.535 5(Diaphragm) ∞ 4.53410 6.137 6 −11.09480 0.70000 1.7804524.1 5.906 7 60.99120 0.92000 6.515 8 85.13520 3.77750 1.88300 40.86.981 9 −15.84300 0.10000 7.345 10 56.48310 2.80000 1.88300 40.8 7.24511 −56.03340 Variable 7.100 12 −455.80430 0.80530 1.67347 28.7 6.820 1318.01680 Variable 6.994 14 50.85540 3.90510 1.88300 40.8 10.297 15−41.00730 (BF) 10.493 Image surface ∞ Various data Focal length 30.0362F-number 1.85425 View angle 19.4978 Image height 10.8150 Overall lengthof lens 55.0786 BF 18.40474 Axial distance data d0 ∞ 943.5114 279.7570d11 1.5000 2.3437 4.3800 d13 6.9800 6.1363 4.1000 Single lens data LensInitial surface Focal element number length 1 1 30.6625 2 3 −51.2410 3 6−11.9770 4 8 15.3973 5 10 32.2319 6 12 −25.7174 7 14 26.2327 Lens unitdata Front Back Initial Overall principal principal Lens surface Focallength points points unit No. length of lens position position 1 127.35203 23.48350 20.73736 17.66640 2 12 −25.71744 0.80530 0.462600.78701 3 14 26.23271 3.90510 1.17145 2.96050 Magnification of lens unitLens Initial unit surface No. ∞ 1000 330 1 1 0.00000 −0.02919 −0.10014 212 4.18502 4.15448 4.09114 3 14 0.26240 0.26224 0.26118

TABLE 3 (Numerical Example 3) Surface data Effective Surface number r dnd vd diameter Object surface ∞ 1 28.87270 1.20000 1.83481 42.7 11.644 211.20020 5.74330 9.257 3 39.14190 1.20000 1.48749 70.4 8.888 4 15.817209.22000 8.353 5 40.19020 5.80000 1.48749 70.4 8.197 6 −17.36590 0.250007.950 7 16.99630 2.23440 1.92286 20.9 6.880 8 23.33040 0.15000 6.473 914.27180 0.90000 1.48749 70.4 6.343 10 9.49870 5.60000 5.92811(Diaphragm) ∞ 4.14220 5.742 12 −13.20030 0.77000 1.90348 23.3 5.663 1354.16530 3.55500 1.83481 42.7 6.183 14 −16.71490 0.15000 6.613 1546.74820 2.98610 1.83481 42.7 6.798 16 −37.73570 Variable 6.800 1729.04120 0.80000 1.84666 23.8 6.940 18 15.15520 Variable 6.888 1927.88570 3.81290 1.71900 53.1 9.033 20 −71.11320 (BF) 9.154 Imagesurface ∞ Various data Focal length 12.2982 F-number 1.85546 View angle41.3302 Image height 9.6300 Overall length of lens 71.7778 BF 16.55704Axial distance data d0 ∞ 926.8299 91.6668 d16 1.5100 1.7487 3.7557 d185.1969 4.9581 2.9511 Single lens data Lens Initial surface Focal elementnumber length 1 1 −22.6181 2 3 −55.3828 3 5 25.7244 4 7 58.0135 5 9−62.0982 6 12 −11.6842 7 13 15.6581 8 15 25.4212 9 17 −38.4517 10 1928.3157 Lens unit data Front Back Initial Overall principal principalLens surface Focal length points points unit No. length of lens positionposition 1 1 13.96609 43.90100 22.18150 55.19111 2 17 −38.45172 0.800000.93061 1.28564 3 19 28.31571 3.81290 0.63502 2.19350 Magnification oflens unit Lens Initial unit surface No. ∞ 1000 160 1 1 0.00000 −0.01494−0.13983 2 17 2.45916 2.45444 2.41394 3 19 0.35808 0.35782 0.35580

TABLE 4 (Numerical Example 4) Surface data Effective Surface number r dnd vd diameter Object surface ∞ 1 417.26590 1.40670 1.48749 70.4 14.0732 15.95220 16.89000 11.552 3 25.41240 4.20000 1.79015 47.8 9.340 4−66.89890 0.25000 8.860 5 13.20950 1.20000 1.48749 70.4 6.900 6 9.136105.41630 6.179 7(Diaphragm) ∞ 4.71000 5.695 8 −9.53450 0.85000 1.6310231.7 5.619 9 43.30240 4.48060 1.73601 53.8 6.438 10 −14.10590 0.150006.960 11 143.14960 2.84160 1.83481 42.7 7.000 12 −34.83740 Variable7.136 13 33.34540 0.77000 1.90426 22.5 7.100 14 16.68380 Variable 7.07415 26.55040 4.38840 1.77250 49.6 9.700 16 −106.12200 (BF) 9.791 Imagesurface ∞ Various data Focal length 16.4891 F-number 1.85519 View angle33.2665 Image height 9.8700 Overall length of lens 71.9424 BF 17.30921Axial distance data d0 ∞ 926.6400 151.9306 d12 1.5260 1.9488 4.0015 d145.5536 5.1307 3.0780 Single lens data Lens Initial surface Focal elementnumber length 1 1 −34.0630 2 3 23.7853 3 5 −67.2696 4 8 −12.3066 5 914.9510 6 11 33.8085 7 13 −37.7534 8 15 27.8935 Lens unit data FrontBack Initial Overall principal principal Lens surface Focal lengthpoints points unit No. length of lens position position 1 1 19.0611142.39520 27.90038 50.02446 2 13 −37.75338 0.77000 0.82741 1.18398 3 1527.89354 4.38840 0.50271 2.37907 Magnification of lens unit Lens Initialunit surface No. ∞ 1000 220 1 1 0.00000 −0.02038 −0.11856 2 13 2.813972.80677 2.76947 3 15 0.30742 0.30691 0.30475

TABLE 5 (Numerical Example 5) Surface data Effective Surface number r dnd vd diameter Object surface ∞ 1 31.39110 8.70000 1.86727 41.4 14.500 2106.05050 0.30000 12.600 3 22.34120 1.96000 1.60227 34.4 11.500 415.19480 11.12020 10.300 5(Diaphragm) ∞ 5.75000 9.031 6 −18.209901.15000 1.79315 23.8 8.628 7 45.78640 1.49080 9.366 8 63.05850 6.454001.88300 40.8 10.130 9 −24.27750 0.10000 10.714 10 49.19470 4.900001.88300 40.8 10.434 11 1674.43050 Variable 9.900 12 −220.09700 0.980001.60463 34.1 8.500 13 23.59130 Variable 8.602 14 78.49360 3.296601.88300 40.8 11.200 15 −51.56840 (BF) 11.318 Image surface ∞ Variousdata Focal length 50.0000 F-number 1.85406 View angle 12.0593 Imageheight 10.8150 Overall length of lens 85.9781 BF 25.61839 Axial distancedata d0 ∞ 1913 461 d11 2.5000 3.6397 7.2784 d13 11.6581 10.5183 6.8796Single lens data Lens Initial surface Focal element number length 1 148.7743 2 3 −87.9381 3 6 −16.2965 4 8 20.5641 5 10 57.3185 6 12 −35.18737 14 35.6697 Lens unit data Front Back Initial Overall principalprincipal Lens surface Focal length points points unit No. length oflens position position 1 1 45.23426 41.92500 36.20086 26.58546 2 12−35.18732 0.98000 0.55077 0.92096 3 14 35.66971 3.29660 1.06928 2.59411Magnification of lens unit Lens Initial unit surface No. ∞ 2000 550 1 10.00000 −0.02376 −0.10004 2 12 4.21740 4.18489 4.09314 3 14 0.262090.26210 0.26131

TABLE 6 (Numerical Example 6) Surface data Effective Surface number r dnd vd diameter Object surface ∞ 1 20.90960 3.48760 1.83481 42.7 8.989 273.31670 0.15000 8.134 3 19.60710 1.00000 1.48749 70.4 7.220 4 9.244605.38590 6.351 5(Diaphragm) ∞ 5.47890 5.884 6 −8.77660 0.72000 1.7446325.4 5.964 7 −133.00140 4.32380 1.88300 40.8 7.039 8 −12.70510 0.150007.704 9 92.02180 2.98800 1.83481 42.7 7.785 10 −34.07470 Variable 7.76111 109.12330 0.80240 1.69419 27.6 6.850 12 19.19240 Variable 6.984 1330.68590 4.12080 1.77250 49.6 10.263 14 −88.81590 (BF) 10.374 Imagesurface ∞ Various data Focal length 26.2626 F-number 1.85576 View angle22.9788 Image height 10.8150 Overall length of lens 56.6628 BF 19.84693Axial distance data d0 ∞ 941.9300 242.7550 d10 1.5100 2.3180 4.6835 d126.6985 5.8904 3.5250 Single lens data Lens Initial surface Focal elementnumber length 1 1 34.0108 2 3 −37.0534 3 6 −12.6505 4 7 15.6445 5 930.1120 6 11 −33.6703 7 13 29.9732 Lens unit data Front Back InitialOverall principal principal Lens surface Focal length points points unitNo. length of lens position position 1 1 26.78155 23.68420 22.4576723.06921 2 11 −33.67030 0.80240 0.57680 0.90385 3 13 29.97319 4.120800.60609 2.36656 Magnification of lens unit Lens Initial unit surface No.∞ 1000 300 1 1 0.00000 −0.02856 −0.11232 2 11 3.51078 3.49510 3.45130 313 0.27932 0.27859 0.27630

The following Table 7 shows the corresponding values to the individualconditions in the inner focus lenses of each of Numerical Examples.

TABLE 7 (Values corresponding to conditions) Numerical Example Condition1 2 3 4 5 6 (1) |f₂/f| 1.262 0.847 3.127 2.290 0.704 1.283 (2) f₂₃/f₁4.943 2.934 5.035 3.564 2.255 3.461 (3) SF −0.048 0.066 0.163 0.021−0.310 −0.026 (4) D₂/{f × tan(ω)} 0.092 0.076 0.074 0.071 0.092 0.072(5) f_(sb)/f 0.820 0.873 1.883 1.386 0.770 0.883 (6) |(1 − β₂) × β₃|0.674 0.836 0.522 0.558 0.843 0.701

The inner focus lens according to the present invention is applicable toa digital still camera, a digital video camera, a camera for a mobileterminal device such as a smart-phone, a surveillance camera in asurveillance system, a Web camera, a vehicle-mounted camera or the like.In particular, the inner focus lens according to the present inventionis suitable for a photographing optical system where high image qualityis required like in a digital still camera system or a digital videocamera system.

Although the present invention has been fully described by way ofexample with reference to the accompanying drawings, it is to beunderstood that various changes and modifications will be apparent tothose skilled in the art. Therefore, unless otherwise such changes andmodification depart from the scope of the present invention, they shouldbe construed as being included therein.

What is claimed is:
 1. An inner focus lens, in order from an object sideto an image side, comprising: a first lens unit having positive opticalpower; a second lens unit having negative optical power; and a thirdlens unit having positive optical power, wherein the second lens unit ismoved along an optical axis so that focusing from an infinite-distanceobject side to a short-distance object side is achieved, the first lensunit includes a bi-convex air lens, and the following conditions (1) and(4) are satisfied:0.65<f ₂ /f|<5.00  (1)0.02<D ₂ /{f×tan(ω)}<0.30  (4) where, f₂ is a focal length of the secondlens unit, f is a focal length of the entire system in an infinityin-focus condition, D₂ is an optical axial thickness of the second lensunit, and ω is a half view angle (°) of the entire system in an infinityin-focus condition.
 2. The inner focus lens as claimed in claim 1,wherein the following condition (3) is satisfied:−0.5<SF<0.5  (3) where, SF=(Ra+Rb)/(Rb−Ra), Ra is a radius of curvatureof an object side surface of the bi-convex air lens included in thefirst lens unit, and Rb is a radius of curvature of an image sidesurface of the bi-convex air lens included in the first lens unit. 3.The inner focus lens as claimed in claim 1, wherein the second lens unitis composed of a single unit having negative optical power.
 4. The innerfocus lens as claimed in claim 3, wherein the single unit havingnegative optical power is composed of one single lens element havingnegative optical power.
 5. The inner focus lens as claimed in claim 1,wherein the following condition (2) is satisfied:0.5<f ₂₃ /f ₁<9.0  (2) where, f₂₃ is a composite focal length of thesecond lens unit and the third lens unit in an infinity in-focuscondition, and f₁ is a focal length of the first lens unit.
 6. The innerfocus lens as claimed in claim 1, having an aperture diaphragm forrestricting axial light beam, wherein the following condition (5) issatisfied:0.5<f _(sb) /f<3.0  (5) where, f_(sb) is a composite focal length oflens elements located on the image side relative to the aperturediaphragm in an infinity in-focus condition, and f is a focal length ofthe entire system in an infinity in-focus condition.
 7. The inner focuslens as claimed in claim 1, wherein the following condition (6) issatisfied:0.2<|(1−β₂)×β₃|<0.9  (6) where, β₂ is a lateral magnification of thesecond lens unit in an infinity in-focus condition, and β₃ is a lateralmagnification of the third lens unit in an infinity in-focus condition.8. An interchangeable lens apparatus comprising: an inner focus lens asclaimed in claim 1; and a lens mount section which is connectable to acamera body including an image sensor for receiving an optical imageformed by the inner focus lens and converting the optical image into anelectric image signal.
 9. A camera system comprising: an interchangeablelens apparatus including an inner focus lens as claimed in claim 1; anda camera body which is detachably connected to the interchangeable lensapparatus via a camera mount section, and includes an image sensor forreceiving an optical image formed by the inner focus lens and convertingthe optical image into an electric image signal.